You're talking about a billionaire who uses Twitter on a daily basis, sends speeches online, looks up and into information on tech giants, hosted a reality TV program and was in several TV shows, and has private and secure White House virtual conferences.
Compared to an old man who is stuck in his basement who reads off of a teleprompter.
The reason why Trump would not want to partake in this would be due to Biden's camp cheating via answers through a teleprompter, offscreen support, and the ability to "cut out" Trump's feed at any inopputrine time and blame it on "technical difficulties".
It should tell you something that during the first debate, Biden's team agreed to be checked for any cheating devices (such as an ear implant) as a request from the Trump team, but then they backed out of it, and it is highly speculated that Biden was in fact, using an earpiece with somebody telling him what to say remotely.